Role of extrac ellular vesicles-mediated communication in the crosstalk between myeloma cells and the bone marrow niche

BACKGROUND-AIM Multiple Myeloma (MM) is characterized by clonal proliferation of PCs in the bone marrow (BM) microenvironment. Here, the interaction between MM cells and BM promotes tumour survival, drug resistance and the development of bone disease. The Notch oncogenic pathway provides a key contribute to the ability of MM cells to shape the BM niche, affecting both MM cell biology and their ability to educate the surrounding normal cells. Recently, extracellular vesicles (EVs) have been reported as novel mediators in creating a supportive milieu for MM. Here we investigate the role of EV-mediated cross-talk in determine MM cells ability to shape the bone marrow niche, promoting the pro-tumor behavior of normal stromal cells. METHODS EVs were isolated by ultracentrifugation and used for functional assays and molecular analysis. EVs characterization was performed by NTA (Nanoparticle Tracking Analysis); qPCR was performed using SYBR Green. Uptake assay was analyzed by confocal imaging. Apoptosis analysis was performed by flow cytometry; evaluation of protein expression was achieved by flow cytometry or western blot. TRAP assay was used to assess osteoclasts differentiation. RESULTS We present evidences that EVs play a crucial role in the dysregulated interactions of MM cells with the BM microenvironment. EVs derived by BM stromal cells (BMSCs) are able to induce resistance to standard of care drugs (i.e. Bortezomib, Melphalan) and can to stimulate MM cells migration. Interestingly, the inhibition of the oncogenic Notch signaling can revert this effect. On the other side, MM-derived EVs are able to increase the production of pro-tumor factors by BMSCs (i.e. SDF1α, IL6) . Finally, EVs released by MM cells are able to carry the main osteoclastogenic factor RANKL and to boost osteoclast differentiation. Consistently, the inhibition of the Notch pathway, one of the key regulator of RANKL production, causes a decrease in MM-EVs pro-osteoclastogenic ability compared with EVs from the control culture. This is particularly relevant due to the crucial role played by bone disease in MM progression. CONCLUSION These new insights in the pathophysiology of the de-arranged BM niche represent the rationale for at therapy aiming to uncouple the crosstalk of MM with the surrounding microenvironment to hamper the progression of this disease.